The present disclosure relates generally to the testing of integrated circuits (ICs), and more particularly to an improved technique for evaluating sub-critical fatigue crack growth in semiconductor devices.
Sub-critical fatigue crack growth generally refers to a phenomenon occurring in materials where microscopic flaws that may be statistically distributed within the material may extend as cracks even under low stress levels. The material when subjected to a repeated stress, which may be constant and/or fluctuating, may fracture and eventually fail due to fatigue. Fatigue induced fractures are typically progressive and grow under the action of the repeated stress. Sub-critical fatigue crack growth is one of the major failure mechanisms of semiconductor and packaging materials used in the fabrication of the semiconductor devices, thereby resulting in reduced reliability and higher costs.
Presently, testing of samples to detect and analyze sub-critical fatigue crack growth is a time intensive process, often taking several days or longer to test one sample. For example, fatigue tests are performed with samples having specific geometry in bending-beam based mechanical tests, such as 4-point bend testing and double cantilever beam testing (DCB). Mechanical stress is repeatedly applied in cycles, such that it may take several hours to test one strip of a multi-strip sample set. All strips are typically measured and averaged to produce a value for that one sample set. As such, testing for sub-critical fatigue crack growth has been generally performed in an academic environment, or applied in industry on a limited basis for materials characterization during new material implementation. It is impractical to apply on a wide basis for routine process characterization and process control.
Recently, laser spallation based adhesion testing techniques have been suggested and are described in further detail in the following United States patent and technical papers, which are hereby incorporated herein by reference into this specification: 1) U.S. Pat. No. 5,438,402, entitled “System And Method For Measuring The Interface Tensile Strength Of Planar Interfaces”, Gupta, 2) “Laser Spallation Adhesion Metrology for Electronic Packaging Development”, Mikel R. Miller and Michael C. Mello, IEEE Electronic Components and Technology Conference, May 2002, (Copyrighted Paper), 3) “A Parametric Study of Laser Induced Thin Film Spallation”, Junlan Wang, Richard L. Weaver, Nancy R. Sottos, Experimental Mechanics Vol. 42, No. 1, March 2002, pages 74-83, Sage Publications, (Copyrighted Paper), 4) “Glass-Modified Stress Waves For Adhesion Measurement Of Ultra Thin Films For Device Applications”, Vijay Gupta, Vassili Kireev, Jun Tian, Hiroshi Yoshida and Haruo Akahoshi, Journal of the Mechanics and Physics of Solids, Volume 51, Issue 8, August 2003, Pages 1395-1412 (Copyrighted Paper), 5) “AE Monitoring From CVD-Diamond Film Subjected To Micro-indentation And Pulse Laser Spallation”, Ikeda, et al., DGZfP-Proceedings BB 90-CD, Lecture 25, 26th European Conference on Acoustic Emission Testing (EWGAE 2004), pages 273-280, and 6) “Tensile And Mixed-Mode Strength Of A Thin Film-Substrate Interface Under Laser Induced Pulse Loading”, Junlan Wang, Nancy R. Sottos, Richard L. Weaver, Journal of the Mechanics and Physics of Solids, Volume 52, Issue 5, May 2004, pages 999-1022. However, traditional laser spallation techniques for testing adhesion properties between two planar interfaces may not be applicable to test and analyze sub-critical fatigue crack growth in semiconductor and packaging materials.